Strain-induced insulator state in La_0.7Sr_0.3CoO_3

We report on the observation of a strain-induced insulator state in ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to enhance the resistivity by several orders of magnitude. Reversible strain of 0.15% applied using a piezoelectric substrate triggers huge resistance modulations, including a change by a factor of 10 in the paramagnetic regime at 300 K. However, below the ferromagnetic ordering temperature, the magnetization data indicate weak dependence on strain for the spin state of the Co ions. We interpret the changes observed in the transport properties in terms of a strain-induced splitting of the Co e_g levels and reduced double exchange, combined with a percolation-type conduction in an electronic cluster state

Wake Geometry Effects on Rotor Blade-Vortex Interaction Noise Directivity

Acoustic measurements from a model rotor wind tunnel test are presented which show that the directionality of rotor blade vortex interaction (BVI) noise is strongly dependent on the rotor advance ratio and disk attitude. A rotor free wake analysis is used to show that the general locus of interactions on the rotor disk is also strongly dependent on advance ratio and disk attitude. A comparison of the changing directionality of the BVI noise with changes in the interaction locations shows that the strongest noise radiation occurs in the direction of motion normal to the blade span at the time of interaction, for both advancing and retreating side BVI. For advancing side interactions, the BVI radiation angle down from the tip-path plane appears relatively insensitive to rotor operating condition and is typically between 40 and 55 deg below the disk. However, the azimuthal radiation direction shows a clear trend with descent speed, moving towards the right of the flight path with increasing descent speed. The movement of the strongest radiation direction is attributed to the movement of the interaction locations on the rotor disk with increasing descent speed

Advancing-side directivity and retreating-side interactions of model rotor blade-vortex interaction noise

Acoustic data are presented from a 40 percent scale model of the four-bladed BO-105 helicopter main rotor, tested in a large aerodynamic wind tunnel. Rotor blade-vortex interaction (BVI) noise data in the low-speed flight range were acquired using a traversing in-flow microphone array. Acoustic results presented are used to assess the acoustic far field of BVI noise, to map the directivity and temporal characteristics of BVI impulsive noise, and to show the existence of retreating-side BVI signals. The characterics of the acoustic radiation patterns, which can often be strongly focused, are found to be very dependent on rotor operating condition. The acoustic signals exhibit multiple blade-vortex interactions per blade with broad impulsive content at lower speeds, while at higher speeds, they exhibit fewer interactions per blade, with much sharper, higher amplitude acoustic signals. Moderate-amplitude BVI acoustic signals measured under the aft retreating quadrant of the rotor are shown to originate from the retreating side of the rotor

Reversible strain effect on the magnetization of LaCoO3 films

The magnetization of ferromagnetic LaCoO3 films grown epitaxially on piezoelectric substrates has been found to systematically decrease with the reduction of tensile strain. The magnetization change induced by the reversible strain variation reveals an increase of the Co magnetic moment with tensile strain. The biaxial strain dependence of the Curie temperature is estimated to be below 4K/% in the as-grown tensile strain state of our films. This is in agreement with results from statically strained films on various substrates

Acoustic measurements from a rotor blade-vortex interaction noise experiment in the German-Dutch Wind Tunnel (DNW)

Acoustic data are presented from a 40 percent scale model of the 4-bladed BO-105 helicopter main rotor, measured in the large European aeroacoustic wind tunnel, the DNW. Rotor blade-vortex interaction (BVI) noise data in the low speed flight range were acquired using a traversing in-flow microphone array. The experimental apparatus, testing procedures, calibration results, and experimental objectives are fully described. A large representative set of averaged acoustic signals is presented

Light interception, gas exchange and carbon balance of different canopy zones of minimally and cane-pruned field-grown Riesling grapevines

Leaf area development, pre-dawn leaf water potential, spatial and temporal patterns of light interception and photosynthesis (A) of minimal pruned (MP) and cane-pruned vertical shoot positioned (VSP) fieldgrown Riesling grapevines were monitored in 2002 and 2003. In order to quantify the contribution of different canopy segments to whole vine carbon gain, diurnal single leaf gas exchange measurements were conducted several times during the season in 8 different canopy segments keeping leaves in their natural position. Carbon losses due to nocturnal respiration (DR) were estimated with a model describing the dependence of DR on temperature. MP vines had about 17 times more but less vigorous shoots with smaller leaves. Leaf area (LA) development was faster for MP than for VSP vines and LA was 2.5-3-fold higher for most of the season. Spatial and temporal patterns of average daily light interception were related to LA development and canopy dimensions for both MP and VSP vines during the first part of the season, but increased independent of LA until mid-October and more so for VSP than MP. Diurnal gas exchange measurements showed differences between canopy segments, measuring dates and systems. Differences between segments were related to light interception in the absence of water deficit, high leaf temperature and vapour pressure deficit. The higher light interception of MP vines caused pre-dawn water potential to decrease faster and to remain at lower levels during most of the season. This limited A more severely for leaves of MP vines in canopy segments which were well exposed to light. The estimated seasonal carbon gain per canopy segment was highest in the apical canopy zones for both canopy systems but carbon assimilation was higher for MP than for VSP vines in all segments with the exception of the interior canopy. Respiratory losses by leaves depended on night temperature and time during the season but generally varied between 3 and 7 % of the amount of carbon gained during the day. MP vines had slightly higher relative respiration losses than VSP vines. On a whole-plant basis, carbon gain of MP vines was between 5.7 (beginning of the season) and 2.2 times (end of season) higher than for VSP vines.